This study proposes evaluate ADPKD patients to: 1)characterize patients at greatest risk for progression to end stage renal disease, 2)determine if MRI as opposed to ultrasound is more reliable and accurate in measuring renal volume and the change in renal volume over time, 3) determine if progression of renal disease in high risk subjects followed early in the course of their disease is better detected by change in renal volume as opposed to change in glomerular filtration rate, and 4) determine if specific mutations in the PKD1 or PKD2 gene are associated with more aggressive phenotype.